Aratani Y, Kitagawa Y
Institute for Biochemical Regulation, School of Agriculture, Nagoya University, Japan.
FEBS Lett. 1988 Aug 1;235(1-2):129-32. doi: 10.1016/0014-5793(88)81247-x.
Tyrosine sulfation of entactin was studied by labeling of 3T3-L1 adipocytes with [35S]methionine or H2 35SO4 in the presence or absence of tunicamycin or monensin. Four precursors (EN1-4) at different steps of modification were detected in addition to mature entactin. Under normal conditions, EN2 and mature entactin were intracellular species, and the latter was sulfated and secreted. Inhibition of co-translational transfer of N-linked oligosaccharides by tunicamycin produced EN1 and EN3 as intracellular species, and EN3 was sulfated and secreted. Interruption of protein transport from medial to trans (distal) Golgi cisternae by monensin, and consequent blockage of terminal glycosylation caused intracellular accumulation of EN4. EN4 was sulfated and of different size compared to mature entactin. These facts suggested that tyrosine sulfation of entactin occurs in medial Golgi cisternae and is not the last modification before its secretion. Our results appeared inconsistent with recent observations by Baeuerle and Huttner [(1987) J. Cell Biol. 105, 2655-2664] that tyrosine sulfation of IgM occurred within the trans (distal) Golgi cisternae as the last modification before its exit from the Golgi complex.
通过在存在或不存在衣霉素或莫能菌素的情况下用[35S]甲硫氨酸或H2 35SO4标记3T3-L1脂肪细胞，研究了巢蛋白的酪氨酸硫酸化。除了成熟的巢蛋白外，还检测到了修饰不同步骤的四种前体（EN1-4）。在正常条件下，EN2和成熟的巢蛋白是细胞内物质，后者被硫酸化并分泌。衣霉素抑制N-连接寡糖的共翻译转移产生了作为细胞内物质的EN1和EN3，且EN3被硫酸化并分泌。莫能菌素中断了蛋白质从高尔基体中间膜囊向反式（远端）膜囊的转运，从而导致终末糖基化受阻，引起EN4在细胞内积累。EN4被硫酸化，且与成熟的巢蛋白相比大小不同。这些事实表明，巢蛋白的酪氨酸硫酸化发生在高尔基体中间膜囊中，并非其分泌前的最后修饰。我们的结果似乎与Baeuerle和Huttner最近的观察结果[(1987) J. Cell Biol. 105, 2655-2664]不一致，他们认为IgM的酪氨酸硫酸化发生在反式（远端）高尔基体膜囊中，是其从高尔基体复合体中排出之前的最后修饰。
